This application claims priority from Korean Patent Application No. 2004-9021, filed on Feb. 11, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a frame-rate converting system, and more particularly, to a method for motion compensated interpolation using overlapped block motion estimation and a frame-rate converter using the method.
2. Description of the Related Art
Conventionally, in personal computers (PC) or high-definition televisions (HDTV), frame rate conversion is performed for compatibility between programs having various broadcasting signal standards such as PAL or NTSC. Frame rate conversion means conversion of the number of frames that are output per second. In particular, when a frame rate is increased, interpolation of a new frame is required. With the recent development of broadcasting techniques, frame rate conversion is performed after video data is compressed according to video compression schemes such as Moving Picture Experts Group (MPEG) or H.263.
Since video signals between frames mostly have high autocorrelation, they have redundancy. Thus, the efficiency of data compression can be improved by removing such redundancy in data compression. At this time, to efficiently compress video frames that temporally change, it is necessary to remove redundancy in the direction of a time axis. In other words, by replacing a frame having little or no motion with respect to a previous frame, it is possible to largely reduce the amount of data to be transmitted. Motion estimation (ME) is a task of searching for the most similar blocks between a previous frame and a current frame. A motion vector (MV) indicates a magnitude of block's movement in ME.
In general, motion estimation methods use a block matching algorithm (BMA) based on the accuracy, the possibility of real-time processing, and hardware implementation.
The BMA divides a seamless input video into pixel blocks of a predetermined size, searches for the most similar block of each of the divided pixel blocks in a previous or future frame, and determines the found block as an MV. To determine similarity between adjacent blocks, mean absolute differences (MADs) are usually used in the BMA.
Also, video signals that are to be inserted between frames are created using the BMA. FIG. 1 shows motion compensated interpolation between frames using the BMA.
In FIG. 1, when pixel values of blocks B included in frames Fn, Fn−, and Fi are fn, fn−1, and fi and a coordinate value included in the frame Fn is x, a video signal to be motion compensation interpolated can be expressed as follows in Equation 1.f1(x+MV(x)/2)={fn(x)+fn−1(x+MV(x))}+2  (1)
Such BMA is suitable for real-time processing, and thus, is used not only in frame rate conversion but also in compression standards such as MPEG2/4 and H.262/264. The BMA shows excellent performance in motion estimation having horizontal/vertical components, but shows inferior performance in rotation or reduction of videos. Therefore, to improve the accuracy using the BMA, the size of a matching block should be increased. However, as a block size increases, the accuracy is improved, but it is difficult to achieve fine expression. As a block size decreases, the amount of computation is decreased and fine expression is possible, but the accuracy is decreased.